Process for the exploitation of bitumenscontaining strata by underground preparation and gasification



Oct.

18, 1966 o H. LANGE ETAL 3,279,540 PROCESS FOR THE EXPLOITATION 0FBITUMENS-CONTAINING STRATA BY UNDERGROUND PREPARATION AND GASIFICATIONFiled Dec. 3, 1962 Prefreafing borehole: eX/end/ng info a bifuminousdepasif by selling off small ekplosions in fhe boreholes.

Heafl'ng hydrocarbons and off in a h em exchanger and injecfing beafeom/Xfures fhereof' fhraugh fhe boreholes in in fhe heafed deposits;

Passing soluf/ons of explosives fhrough fhe barb/voles info Ihe heafedh/fum/naus depasif fa precip/fafc fhe, exp 5W.

Passing a ho/ fluid through fhe boreholes fo evaporate fhe so/vents.

lgnl'fl'n 9 M c eXp/us/WJS.

INVENTORS HANS LANGE GUNTHER SCHLICf/T deceased,

Woo/1m ATTOR NEYS United States Patent PROCESS FOR THE EXPLOITATION 0FBITUMENS- CONTAINING STRATA BY UNDERGROUND PREPARATION AND GASIFICATIONHans Lange, Wietze, Kreis Celle, Germany, and Gunther Schlicht,deceased, late of Hamhurg-Othmarschen, Germany, by Erika Marie ElisabethSchlicht, legal representative, Hamburg-Othmarschen, Germany, assignorsto Deutsche Erdiil-Aktieugesellschaft, Hamburg, Germany Filed Dec. 3,1962, Ser. No. 242,868 Claims priority, application Germany, Dec. 5,1961, Sch 30,662, Sch 30,663 2 Claims. (Cl. 16636) This inventionrelates to an improved method in the extraction of bitumens from theground, and as such is related to copending applications Ser. Nos.215,493, filed August 6, 1962; 216,702, filed August 6, 1962, and nowUS. Patent No. 3,236,739; and 215,494, filed August 6, 1962, now US.Patent No. 3,242,989.

A process for the exploitation of bitumens-containing strata utilizes anunderground generator, in which a heattransfer medium is introducedunder pressure over a reactor into a treatment borehole. By this methodthe bitumens in the underground strata are dislodged and heated so as toform energy-rich masses which can produce or be converted into gases.This underground generator is bounded by so-called cleavage line'borings, and in conjunction with the treatment borings is divided intoa plurality of treatment sections which can be worked simultaneously orsuccessively. This is possible because the heat which is introducedthrough the treatment borings will have to follow predetermined paths inits passage through the strata. Only in this manner has it becomepossible for the heat which has spread out laterally from the treatmentborings to be brought as initial heat to the strata to be gasified, andafter g-asification of one such section of the underground generator tomake use of the stored heat in the upper strata for preheating thegasification air that is on its way to the other sections of theunderground generator.

The burning and gasification zone of the underground generator thusreceives at every time and in every subsection, additional heat, wherebyit is kept at a high temperature and provides a well preheated roofstructure so that the advancing burning and gasification zone can alwaysbe kept at an advantageously high temperature.

This reaction heat from the underground generator, which has beenintensified by uncontrolled nuclear fission, and which has a high energyvalue, can be referred to as double thermal impact.

If this uncontrolled nuclear fission in the reactor cannot or must notoccur, then the coal will not be subjected either to the powerfulmechanical shock or to the increased heat.

After failure of the second thermal impact, the ensuing gasificationprocess will go on more slowly and at a lower temperature, so that inthe temperature region at 340-425" C., the coal will :be softened over awider region. In this manner it will be possible to diminish or evenreverse the fissure or pore formation which has been started, as wheninadequate yield or poor quality of the gas is a problem.

It is an object of this invention to use various measures and steps tocorrect the unfavorable effects on the gasification process which resultfrom an inadequate disruption of the coal after failure of the secondthermal shock.

Upon further study of the specification and appended claims, otherobjects and advantages of this invention will become apparent.

To attain these objects, there. is provided a modified procedure whichwill be referred to as py-ropneumatic thermal shock. It is defined asfollows:

(1) As a preliminary step, the introduction of gases into the stratatogether with the heat transfer medium, the gases being deposited asbubbles in the fissures or pores so that they can be compressed byincreased pressure, .but upon reduction of pressure will themselvesexp-and and thereby clear out the fissures and pores; and

(2) As a principal step, the introduction of O -carriers and/orexplosives in dissolved form, their precipitation, and fixing of same infissures and cracks, and their subsequent elimination by localcombustions or explosions so as to cause fissure formation and increasedgaseous pressure in the strata.

(The materials are introduced into the strata through boreholes whichare generally vertical. If the work is being done from shafts orexcavations, then the boreholes are generally horizontal.)

In the figure a flow sheet of a particular embodiment of the inventionis illustrated.

With respect to the details of the preliminary step, condensiblehydrocarbons are used as the heat transfer media, and are passed througha heat exchanger for receiving heat (about 350 C.) from a heat sourcesuch as an atomic reactor, and under pressure sufficient to break theunderground deposits (about 20-35 atm. per 100 m. depth), so that theheat can advance into the strata. Preferably, the hydrocarbon shouldhave a normal boiling point of about not less than 50 C. Specificexamples of such hydrocarbons are benzene or a mixture of 10% pentane,25% hexane and 65% heptane, or a mixture of 15% pentane and heptane.

In addition, it is necessary to employ incondensable gases such an inertgases, light hydrocarbons such as methane, and gaseous oxygen or air inthe heat transfer medium in predetermined amounts. These added materialswill increase the volume of the heat transfer va- =pors and willtherefore increase the depth of penetration thereof into the fissuresand cracks of the strata beyond where pure gases would penetrate, andupon condensation will cause the deposition of large numbers of tinyglobules which will furnish many points of support for the adjacentsurfaces. It is thus apparent that the incondensible gases must remaingaseous under 200 atm. (absolute) pressure and temperature as low as 150C. The ratio of condensibles to incondensibles, on a weight basis, isabout parts condensibles to about 30 parts, preferably 20 partsincondensibles.

After the strata have been loosened by means of pressure and thermalliquids and gases in the region of the underground generator, smallerexplosions may be set off in the boreholes. The strata are then exposedto pressure waves from the cleavage line borings and also to the weightof the formations above, which will cause the entrapped gaseous globulesto become compressed and thus serve to store up energy. After passage ofthe pressure waves, these entrapped globules expand so as to restore theporosity and open up the crevices which existed previously.

After this preliminary treatment, oxygen carriers such as potassiumnitrate or dissolved explosives are introduced with the heat transfermedium into the strata and distributed over a wide region. Suitable heattransfer materials are hydrocarbon fractions with different boiling.points, and eventually also with separated boiling points so thatseparate condensations will occur. As a principal heat transfer mediumthere is preferably used a hydrocarbon fr-action which under 1 atm. hasa boiling point of 2503()0 C. Since the heat transfer medium of thisinvention is always under a certain positive pressure in the strata, itwill remain liquid in the heat exchanger of presence of combustiblegases. Explosive blasting materials will also cause gas formation with abreaking up of the strata. The explosive charges in the cleavage guidingholes are preferably set off simultaneously. As preferred oxygencarriers or explosives there can be mentioned TNT, black powder or amixture of 1 kg. benzene and 1.1 kg.'oxygen 95%.

As a modification of this process, a small preliminary explosion may beset off in the boreholes that have not yet been line-d with tubes whichwill initiate the formation of fissures in the immediate surroundings.After the boreholes are redrilled, the fissures and boreholes are againfilled with dissolved explosives so that the principal explosion thusproduced will exert a strongly propagated disrupting action in thestrata.

As solvents for the oxygen producing substances or explosives, certaincomponents of the heat transfer medium that is sent to the treatment orcleavage guiding medium m'ay be used. By gradual or sudden changes inthe compositions of its components, the heat transfer agent can also bemade to serve as a solvent. Low boiling hydrocarbons are primarilysuitable for this purpose, depending on the desired kind of action.Examples of preferred solvents are benzene, xylol and toluol.

The transport of the oxygen oarrier or the explosive and its fixation isaccomplished as follows: A heat transfer medium, after passage throughthe heat exchanger of a reactor, is introduced into the strata which arepartly opened up by fissure formation, warming and partial degassing. Ifthe reactor is only to give off heat, and the uncontrolled nucleardisintegration, as above mentioned, cannot or must not be brought about,then the reactor can obviously be substituted by some other source ofheat, as for example an electrically energized immersion heater or by aheat exchanger supplied by heat from another source.

After the required operation has commenced, a low boiling solvent isintroduced cold into the strata after having by-passed the heatexchanger. After the strata have been locally cooled in that manner, asolution of an oxygen liberating substance or an explosive in a volatilesolvent is introduced until it has reached the required distance fromthe borehole, the distance having been calculated with due considerationto the subsequent introduction of the heat carrying medium. The heattransfer medium is then introduced, which after a certain time, willvaporize the solvent that was used for introducing the oxygen liberatingsubstance or the explosive, so that these materials will now be presentin highly effective form. The dissolved explosive is relatively safe tohandle. If the separation of the explosive by vaporization is impossibleor impractical, then use is made of a solvent which upon mixture withanother subsequently introduced solvent will cause precipitation of theexplosive or the oxygen carrier.

If a formation that has been thus treated with heat and explosivesbecomes plastic and difiicultly permeable in places, the entrapped gasbubbles or the products of combustion of the introduced hydrocarbons, orof those from the formation, or the gases from the detonated explosives,will cause the strata to again become partly porous after the pressurehas been removed.

In some formations with solid bitumens, it may not be possible toproduce adequate fissures by means of small explosives and pressurewaves. The widely varied structure of coal, the varying depths of coaldeposits, andthe different thicknesses of its; beds, lead to a widevariety of conditions, and it is therefore necessary to increase thefissure formation which has been initiated by theuse of vapors.

This can be accomplished by thermal stresses in the formation, whichwill cause the formation of fissures and will enlarge or supplement thefissures which have been produced by pressure and explosions. Thermalstresses occur when heat is delivered quickly into a restricted portionof the formation, which will produce large temperature differences inclosely adjacent portions of the bitumen or coal. There will then be hotregions in the fissures in immediate proximity to cold regions. Theresulting thermal stresses will produce more fissures, as can beobserved during the heating of coal in retorts or coke ovens.

For this purpose it is necessary that a large quantity of heat beintroduced quickly into the formationand across long and numerous paths.This is accomplished by a pneumatically accumulated thermal shockdelivering a large amount of heat by means of vapors and gases.

The amount of energy that is introduced by a heated liquid isconsiderable. liquid under 320 atm. pressure causes fissure formationover a circumference of m. around the treatment borehole. If, however,vapors or gases are used instead of the liquid, and are introduced underthe same pressure, there will be stored in the formation about 75 m. 320atm.=24,000 m. of gases and vapors under pressure.

If the energy of the source of heat is not equal to the energy desiredto be stored, then additional heat can be produced by igniting andburning the hydrocarbon and air mixture which passes from the treatmentborehole into the formation. This additional burning is continued untilthe frictional resistance of the opened fissures has become so smallthat the gasification and vaporization can itself be omitted, with theinjection of air aloneinto the formation.

If the formation is to be rendered porous by fissureand and poreformation between the treatment-borehole and the cleavage directingboreholes by heat and pressure alone and without additional nuclearexplosions, then inert gases or air must be added to the medium whichdelivers heat to the introduced hydrocarbons, and in amounts suflicientto produce strata-supporting bubbles. In order to introduce the largequantities of this gas-air mixture into the treatment boreholes in themost efiicient manner, and to have convenient control over it both atthe inlet and at the outlet end of the treatment borehole, it may beadvantageous to perform some preparatory operations in both thetreatment and the cleavage guiding boreholes.

For this purpose a small explosion is set off in each borehole toproduce fissures in the immediate neighborhood of the borehole forincreasing the free surface in that region.

After these explosions, the holes are redrilled and lined with casings.In every treatment borehole certain masses:

of liquid hydrocarbons loaded with gases for producing strata supportingbubbles are injected under a pressure greater than the disruptionpressure of theformation, whereby fissure formation will be increasedand extended while the gaseous bubbles will keep the fissures open.

It is not considered practical to carry out such treatments with largermasses of liquids (about 0.25 liter. per cm. carbon) becauseincompressible liquids will quickly break through any boundary. Thepressure actionwill then be of only short duration and willspontaneously. drop off as soon as a fissure extends all the way over toa cleavage directing borehole so that additional fissureswill not beformed, at least not at any great distance from the. treatment borehole.Only one such fissure will prevent such an underground enerator frombeing operated successfully because it will then be impossible tocontrol the movement of gases and vapors.

Injection of 75 .m. of a pure If now instead of a liquid, a gas isinjected into the coal stratum, it will, because of its much lowerviscosity, penetrate into tiny capillary fissures and microscopic pores.Since it is compressible, it will store up a substantial amount ofpressure-energy, even though the pressure may increase only slowly. Ifthe breaking strength of the formation is exceeded, then fissureformation will result. The pressure, however, drops only slightly, andwill be brought up again until the initially produced fissure reaches acleavage directing borehole. The large amount of stored up gas stillcontains much pressureenergy, which continues to act on all sidesandwill produce fissures which will lead to the other cleavage directingboreholes. The accumulation of vapors and gases will thus cause thedisruption process to continue for a long time. If the compressed fluidshave much heat stored up in them, then they will pass more quicklythrough the larger fissures and thus produce strong local heating, whichwill result in thermal stresses between these hot regions and adjacentcooler regions, and that will in turn lead to the formation of morefissures.

In recapitulation, it may be stated that the last-described process,which does not involve the setting off of any powerful blasts, iscarried out by first pretreating the boreholes to disrupt the formationsin their immediate neighborhoods, and then passing vaporized or liquidhydrocarbons, steam and gases such as air over a heat-exchanger and theninto a treatment borehole under a pressure greater than the disruptionpressure of the formation, until a fissure has broken through under highpressure to a cleavage directing borehole.

In the ensuing second phase, which is characterized by high heatproduction, the mixture of hydrocarbon vapors and air that leaves thetreatment borehole is ignited and generates a substantial amount of'heatduring the time that it burns. The thermal strains produced in thismanner cause a widening of the fissures and increased porosity of thecoal.

The ignition of the mixture can b effected either by means of anelectrically operated igniter, or by a short time admixture of vaporswith an ignition point below the surface temperature of the heatexchanger. Combustion can also be initiated by the use of platinumblack.

In this second phase, the expansion of the forced-in air which hasresulted from the generation of heat has reduced the quantity ofhydrocarbons to such an extent that there will be present an excess ofoxygen which will prevent any occurrence of rust which could causeclogging of the fixtures. To compensate for the diminishing supply ofsteam at the source of heat, additional water is added for conversioninto steam. In porous formations the steam or the water, possibly mixedwith hydrocarbons which could be very viscous, may conveniently beintroduced through a separate pipe into the formations in which the pipepasses through a packer which separates the upper space where air oroxygen-enriched air is used for burning the light hydrocarbons, from thelower space where the second phase is carried out. The movement of thelighter materials in the upper space assist in the movement of thematerials in the lower space in the region of the treatment borehole, asin a direction toward a cleavage guiding hole. During the early part ofthe steaming process, a water gas reaction may occur.

The second phase ends when the section that is being treated withpressure and heat has acquired the necessary porosity. In order to avoida deterioration of the heating value of the vaporization gas byadmixture with the products of combustion from the second phase, itshould be terminated as quickly as possible. A time period of about 4days should be sufficient.

Still another modification includes circulating the heat transfer fluidbetween the borings leading to the upper strata of the formation. Theheat transfer medium which has broken through to the cleavage directingborings is brought above ground to be reheated, and is then returned tothe treatment borehole for another passage from the treatment to thecleavage directing borehole. This medium, which is now enriched withhydrocarbons, and from which no products have been separated, iscontinued in circulation until the desired effect is produced. Such aneffect consists of a heating up of the formation together with increasedpermeability and/or porosity. As heat carriers, gaseou hydrocarbonsmixed with liquid hydrocarbons of widely different boiling points may beused.

In the third phase which has now commenced, air alone which has beenpreheated at the combustion front of the second phase is introduced forvaporizing and degasing the bituminous formations. From thi point on,the process continues as described in our copending patent applicationSerial No. 216,271, filed August 7, 1962.

Without further elaboration, it is believed that one skilled in the artcan employ this invention to full advantage. Consequently, the followingpreferred specific embodiments are to be considered exemplary and not inany way limitative of the remainder of the specification and appendedclaims.

Example I A coal stratum of brittle mineral coal having a thickness of1.50 m. is deposited in a depth of 320 in. A heat source, for instance apower reactor, evaporates in the pressure bore under simultaneousemission of radiation energy, e.g. of of heat energy and 10% ofradiation energy with 500,000 kcaL/h. for preheating for 25 days, 500kg. of liquid hydrocarbons having a large boiling range, for instance10% pentane, 25% hexane, 65% heptane and 3,000 Nm. /h. of compressedair, to 320 C. at a pressure of 90 atmospheres absolute. At thispressure the coal cracks and therefore, if said pressure is maintained,the hydrocarbon flows through the coal stratum. The vaporoushydrocarbons are condensed at the newly formed surfaces of the crevicesin the direction of the depth of the layer according to the boilingpoint of the individual hydrocarbons and retain the compressed air ofthe mixture in a large number of bubbles as supports within thecrevices. When an ignition is caused in the pressure bore after 25 days,the oxygen of the compressed air burns as much coal in the cracks thatthe temperature in said crevices rises to more than 450 C., whereby thecoal is degasified in said cracks and causes the production ofstationary permeable coke. Thereafter, a further progressingdegasification and gasification is possible, for instance, with 12,000Nmfi/h. to obtain heated air enriched with 85% of oxygen at a pressureof 15 atmospheres absolute at 300 C. until the coal is completelygasified in the underground generator. The generator gas has a pressureof 12 atmosphere absolute, and per 1 kg. of coal there are produced 2.05Nm. of generator gas having a heating value of 2,800 kcaL/mfi.

Example II A coal deposit consisting of tough elastic mineral coal andhaving a thickness of 2.20 m. is deposited at a depth of 750 m. A heatsource evaporates in the pressure bore at a ratio of 500,000 kcaL/h. forpreheating for 2-5 days 500 kg./h. of liquid hydrocarbons having a largeboiling range according to Example I, and 3,000 Nmfi/ h. of compressedair to 300 C. at a pressure of M0 atmospheres absolute. At said pressurethe coal becomes cracky, but the cracks close immediately after thepressure falls below the cracking pressure. In this case the supportingbubbles alone are not able to keep the cracks open. In order to obtain adepth effect, the surroundings of the pressure bore are cooled down to atemperature less than C. after the preheating by means of coldhydrocarbons, so that a solution of 200 kg. of explosive TNT containingthe threefold quantity of toluene and the 12 fold quantity of benzenecanrbe distributed in the cracks formed within the pressure bore. Afterthese explosives are dis tributed, compressed air in a quantity of 3,000Nm. /h.

at 240 atmospheres absolute and evaporated liquid hydrocarbons of alarge boiling range in a quantity of 500 kg./h., for instance, 15% byweight of pentane and 85% by weight of heptane, are preheated again to atemperature up to 300 C., whereby the solvents of the explosive areevaporated to such an extent that from the preheating temperature anauto-ignition of the explosives distributed in the coal occurs, wherebythe temperature in the cracks increases to such an extent, that adegasification occurs and the fusing temperature is exceeded. A heavy,pervious coke is obtained thereby, which makes it possible to initiatethe degasification by means of air enriched with oxygen at a pressure of15 atmospheres absolute.

Example III The three uppermost meters of a mineral deposit having athickness of 5 I11. and being positioned at a depth of 1200 rn. have apermeable structure, whereas the structure of the 2 lowermost meters iscoalesced or scarcely permeable. One operates in the upper portion ofthe pressure bore with a disruption pressure of 360 atmospheresabsolute, and for the rest as described in Example I. Cold mixturesconsisting of 1.57 kg. of per 1 kg. of hydrocarbons, as for instancebenzene, are introduced at a quantity of 500 'kg./ h. per 1 kg. ofthickness of the scarcely permeable deposit into the lower portion ofthe deposit at the disruption pressure through a separateconduit andthrough a bore arranged in the lower portion of the packer, for 5-6days. However, it is also possible to use the same quantities of amixture consisting of 3 parts of water and 7 parts of lighterhydrocarbons, as for instance, heptane. Through the progressinggasification in the upper portion of the deposit the occluded liquidsare heated and caused to ignite or evaporate, whereby the lower portionof the deposit is developed for removal of the minerals.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions. Consequently, such changes and modifications are properly,equitable, and intended to be, within the full range of equivalence ofthe following claims.

What is claimed is:

1. In a process for the recovery of solid bitumens from undergroundstrata deposits, the steps of:

(a) injecting through boreholes leading into said strata a heatedmixture of non-condensible gases and condensible hydrocarbons at apressure above the fracturing pressure of said strata whereby said condensible hydrocarbons are condensed in the cooler portions of saidstrata with the formation of bubbles r of non-condensible gases in thefissures;

(b) passing into said strata along with a heat transfer medium a memberselected from the group consisting of oxygen-releasing compositions andexplosives, said member dissolved in volatile solvents whereby saidmember is precipitated in said strata in a highly re-. active condition;

(0) evaporating said solvents by subsequently introdusing a hot fluidmedium; and

(d) igniting said member.

2. In a process for the recovery of solid bitumens from undergroundstrata deposits, the steps of;

(a) preheating boreholes extending into said strata with smallexplosions;

(b) heating hydrocarbons together with steam and a given quantity of airby passage through a heatexchanger and forcing said heated hydrocarbons,steam and given quantity of air through said boreholes at a pressureabove the fracturing pressure of said strata whereby said hydrocarbonsare condensed in the coolerportions of said strata with the formation ofbubbles of said steam and air in the fissures untiLa break-through in anadjacent cleavage directing bore-- hole is effected;

(c) thereafter increasing said given quantity of air;

and (d) igniting the mixture of said hydrocarbons with steam and airresulting in underground combustion and heating of the formation wherebysubject to the breakthrough the gaseous volume is increased ReferencesCited by the Examiner JACOB L. NACKENOFF, Primary Examiner.

BENJAMIN HERSH, CHARLES E. OCONNELL,

Examiners. S. J. NOVOSAD, Assistant Examiner.

1. IN A PROCESS FOR THE RECOVERY OF SOLID BITUMENS FROM UNDERGROUNDSTRATA DEPOSITS, THE STEPS OF: (A) INJECTING THROUGH BOREHOLES LEADINGINTO SAID STRATA A HEATED MIXTURE OF NON-CONDENSIBLE GASES ANDCONDENSIBLE HYDROCARBONS AT A PRESSURE ABOVE THE FRACTURING PRESSURE OFSAID STRATA WHEREBY SAID CONDENSIBLE HYDROCARBONS ARE CONDENSED IN THECOOLER PORTIONS OF SAID STRATA WITH THE FORMATION OF BUBBLES OFNON-CONDENSIBLE GASES IN THE FIGURES; (B) PASSING INTO SAID STRATA ALONGWITH A HEAT TRANSFER MEDIUM A MEMBER SELECTED FROM THE GROUP CONSISTINGOF OXYGEN-RELEASING COMPOSITIONS AND EXPLOSIVES, SAID MEMBER DISSOLVEDIN VOLATILE SOLVENTS WHEREBY SAID MEMBER IS PRECIPITATED IN SAID STRATAIN A HIGHLY REACTIVE CONDITION; (C) EVAPORATING SAID SOLVENTS BYSUBSEQUENTLY INTRODUCING A HOT FLUID MEDIUM; AND (D) IGNITING SAIDMEMBER.